The variational statement of the problem (REF )–(REF )
appeals to the integral identity [1]}
\(\begin{array}{c}(\nabla _xU^\varepsilon ,\nabla _xV^\varepsilon )_{\varpi ^\varepsilon }=\Lambda ^\varepsilon (U^\varepsilon ,V^\varepsilon )_{\varpi ^\varepsilon }\quad \forall V^\varepsilon \in H^{1,\eta }_{per}(\varpi ^\varepsilon ),\end{array}\) 
